Process for steam cracking heavy hydrocarbon feedstocks

Abstract

A process for feeding or cracking heavy hydrocarbon feedstock containing non-volatile hydrocarbons comprising: heating the heavy hydrocarbon feedstock, mixing the heavy hydrocarbon feedstock with a fluid and/or a primary dilution steam stream to form a mixture, flashing the mixture to form a vapor phase and a liquid phase, and varying the amount of the fluid and/or the primary dilution steam stream mixed with the heavy hydrocarbon feedstock in accordance with at least one selected operating parameter of the process, such as the temperature of the flash stream before entering the flash drum.

1. A process for cracking a heavy hydrocarbon feedstock in a furnace having at least a convection section and a radiant section; said process comprising:
 (a) heating said heavy hydrocarbon feedstock in said convection section to form a heated feedstock; 
 (b) introducing a fluid and steam to said heated feedstock to form a mixture; 
 (c) heating said mixture in said convection section to form a heated mixture; said heated mixture having a vapor phase and a liquid phase; 
 (d) substantially separating said vapor phase and said liquid phase; 
 (e) feeding the separated vapor phase to said radiant section to crack at least a portion of hydrocarbons in said separated vapor phase; 
 (f) varying the rate of introduction of said fluid and the rate of introduction of said steam in response to changes in at least one operating parameter of said process to maintain the ratio of said separated vapor phase to the separated liquid phase substantially constant. 
 
     
     
       2. The process of  claim 1 , wherein said at least one operating parameter of said process is at least one of: the temperature of said heated mixture; the pressure of said heated mixture; the flow rate of said heated mixture, the quantity of oxygen in the flue gas of said furnace; the concentration of volatiles in said heavy hydrocarbon feedstock; and the furnace load. 
     
     
       3. The process of  claim 2 , further comprising monitoring said at least one operating parameter. 
     
     
       4. The process of  claim 1 , further comprising monitoring said ratio of said separated vapor phase to the separated liquid phase by monitoring the temperature of said heated mixture. 
     
     
       5. The process of  claim 1 , wherein said fluid comprises at least one of liquid hydrocarbon and water. 
     
     
       6. The process of  claim 1 , wherein said fluid comprises water. 
     
     
       7. The process of  claim 6 , further comprising maintaining the hydrocarbon partial pressure of said mixture substantially constant. 
     
     
       8. The process of  claim 7 , further comprising holding the sum of the rate of introduction of water and the rate of introduction of steam substantially constant. 
     
     
       9. The process of  claim 8 , further comprising using the heat of vaporization of water to control the temperature of said heated mixture after step (c) but prior to step (d). 
     
     
       10. The process of  claim 1 , wherein secondary dilution steam is superheated in said convection section and then mixed with said mixture before said flash. 
     
     
       11. The process of  claim 10 , wherein a portion of said secondary dilution steam is mixed with said heated mixture before step (c) and another portion of said secondary dilution steam is mixed with said separated vapor phase. 
     
     
       12. The process of  claim 1 , wherein about fifty percent (50%) to about ninety-five percent (95%) of hydrocarbons in said heavy hydrocarbon feedstock are in said separated vapor phase. 
     
     
       13. The process of  claim 1 , wherein at least a portion of said separated vapor phase is heated in said convection section to form a heated vapor phase and said heated vapor phase is fed to said radiant section in step (e). 
     
     
       14. The process of  claim 13 , wherein the temperature of said heated vapor phase is from about 800° F. (430° C.) to about 1200° F. (650° C.). 
     
     
       15. The process of  claim 1 , wherein said heavy hydrocarbon feedstock comprises at least one of steam cracked gas oil and residues, gas oils, heating oil, jet fuel, diesel, kerosene, gasoline, coker naptha, steam cracked naphtha, catalytically cracked naphtha, hydrocrackate, reformate, raffinate reformate, Fischer-Tropsch liquids, Fiseher-Tropsch gases, natural gasoline, distillate, virgin naphtha, crude oil, atmospheric pipestill bottoms, vacuum pipestill streams including bottoms, wide boiling range naphtha to gas oil condensate, heavy non-virgin hydrocarbon streams from refineries, vacuum gas oils, heavy gas oil, naphtha contaminated with crude, atmospheric resid, heavy residium, C4's/residue admixture, and naphtha residue admixture. 
     
     
       16. The process of  claim 1 , wherein said heavy hydrocarbon feedstock comprises low sulfur waxy resid. 
     
     
       17. The process of  claim 1 , wherein about sixty percent (60%) to about eighty percent (80%) of said heavy hydrocarbon feedstock has a boiling point below about 1100° F. (590° C.). 
     
     
       18. The process of  claim 1 , wherein said heavy hydrocarbon feedstock has a nominal final boiling point of at least about 600° F. (320° C.). 
     
     
       19. The process of  claim 1 , wherein said vapor phase has a nominal end boiling point below about 1400° F. (760° C.). 
     
     
       20. The process of  claim 1 , wherein the temperature of said heated mixture is from about 600° C. (320° C.) to about 950° F. (510° C.). 
     
     
       21. The process of  claim 1 , wherein step (d) occurs in at least one flash drum. 
     
     
       22. The process of  claim 21 , wherein the pressure of said at least one flash drum is operated between about (280 kPaa) and about 200 psia (1380 kPaa). 
     
     
       23. The process of  claim 1 , wherein said fluid and said steam are introduced to said heated heavy hydrocarbon feedstock using a double sparger assembly. 
     
     
       24. The process of  claim 23 , wherein said double sparger assembly minimizes hammer of said steam and said water in the heat exchange tubes of said convection section. 
     
     
       25. A steam cracking process using a furnace and a flash drum, said furnace having at least a convection section and a radiant section, for processing heavy hydrocarbon feedstock; said process comprising:
 (a) heating said feedstock in said convection section to form a heated hydrocarbon stream; 
 (b) introducing water and steam to said heated hydrocarbon stream to form a mixture stream; 
 (c) heating said mixture stream in said convection section to form a heated mixture stream having a vapor phase and a liquid phase; 
 (d) substantially separating said vapor phase and said liquid phase in said flash drum; 
 (e) heating said separated vapor phase in said convection section to form a heated vapor phase; 
 (f) feeding said heated vapor phase to said radiant section to crack at least a portion of hydrocarbons in said heated vapor phase; 
 (g) varying the flow rate of said water and said steam in response to changes in at least one operating parameter of said process; and 
 (h) holding the sum of said water flaw rate and said steam flow rate substantially constant to maintain the ratio of said separated vapor phase to said separated liquid phase substantially constant. 
 
     
     
       26. The process of  claim 25 , wherein said at least one operating parameter of said process is at least one of: the temperature of said heated mixture stream; the pressure of said heated mixture stream; the flow rate of said heated mixture stream, the quantity of oxygen in the flue gas of said furnace; the concentration of volatiles in said heavy hydrocarbon feedstock; and the furnace load. 
     
     
       27. The process of  claim 26 , further comprising monitoring said at least one operating parameter. 
     
     
       28. The process of  claim 26 , further comprising monitoring said ratio of said separated vapor phase to said separated liquid phase by monitoring the temperature of said heated mixture stream. 
     
     
       29. The process of  claim 25 , further comprising maintaining the hydrocarbon partial pressure of said heated mixture stream substantially constant. 
     
     
       30. The process of  claim 29 , further comprising utilizing the heat of vaporization of water to control the temperature of said heated mixture stream. 
     
     
       31. The process of  claim 25 , wherein a secondary dilution steam stream is superheated in said convection section and then mixed with said heated mixture stream. 
     
     
       32. The process of  claim 31 , wherein a portion of said secondary dilution steam is mixed with said heated mixture stream and another portion of said secondary dilution steam is mixed with said separated vapor phase. 
     
     
       33. The process of  claim 25 , wherein about fifty percent (50%) to about ninety-five percent (95%) of hydrocarbons in said heavy hydrocarbon feedstock are in said separated vapor phase. 
     
     
       34. The process of  claim 25 , wherein the temperature of said heated vapor phase is from about 800° F. (430° C.) to about 1200° F. (650° C.). 
     
     
       35. The process of  claim 25 , wherein said heavy hydrocarbon feedstock comprises at least one of steam cracked gas oil and residues, gas oils, heating oil, jet fuel, diesel, kerosene, gasoline, coker naphtha, steam cracked naphtha, catalytically cracked naphtha, hydrocrackate, reformate, raffinate reformate, Fischer-Tropsch liquids, Fischer-Tropsch gases, natural gasoline, distillate, virgin naphtha, crude oil, atmospheric pipestill bottoms, vacuum pipestill streams including bottoms, wide boiling range naphtha to gas oil condensate, heavy non-virgin hydrocarbon steams from refineries, vacuum gas oils, heavy gas oil, naphtha contaminated with crude, atmospheric resid, heavy residium, C4's/residue admixture, and naphtha residue admixture. 
     
     
       36. The process of  claim 25 , wherein said heavy hydrocarbon feedstock comprises low sulfur waxy resid. 
     
     
       37. The process of  claim 25 , wherein about sixty percent (60%) to about eighty percent (80%) of said heavy hydrocarbon feedstock has a boiling point below about 1100° F. (590° C.). 
     
     
       38. The process of  claim 25 , wherein said heavy hydrocarbon feedstock has a nominal final boiling point of at least about 600° F. (320° C.). 
     
     
       39. The process of claim wherein said separated vapor phase has a nominal end boiling point below about 1400° F. (760° C.). 
     
     
       40. The process of  claim 25 , wherein the temperature of said heated mixture stream is from about 600° F. (320° C.) to about 950° F. (510° C.). 
     
     
       41. The process of  claim 25 , wherein the pressure of said at least one flash drum is operated between about 40 and 200 psia (280 kPaa) and about 200 psia (1380 kPaa). 
     
     
       42. The process of  claim 25 , wherein said water and said steam are introduced to said heated heavy hydrocarbon feedstock using a double sparger assembly. 
     
     
       43. The process of  claim 42 , wherein said double sparger assembly minimizes hammer of said steam and said water in the heat exchange tubes of said convection section.